What is THAT?
Last week we spent a wonderful part of a day at Griffiths-Priday State Park near Copalis, WA. When we arrived at the parking lot, we were stymied - a wide, deep creek separated us from the beach. Luckily, a kind local with a sweet dog directed us to the trail heading north and around the mouth of the creek - about a 3/4 mile walk. He told us that the creek's mouth has been migrating north over the years. At one point, it was south of the parking area. Someday it might connect to the Copalis River and cut off the beach access altogether. For now, though, you can walk along the edge of the dunes and down on to the beach. It was almost deserted, and there were no cars at all. There were shells and sand dollars on the beach - including the first scallop shells I've ever found. And then I found this:
It was about 9 inches long, and rubbery, but sturdy enough that I could scoop it up with a stick and carry it. It was partly transparent. One side was flattened, and the other rounded. The rounded side had a bump; there appeared to be organs visible inside the bump. Its skin was scattered with bumps. But what was it?? I thought maybe a sea cucumber, but it's not radially symmetrical. It wasn't like any nudibranch I'd ever heard of. Maybe a squid, with the tentacles gone? No, no eyes. So not a fish either. Maybe an organ of something larger? But it had that rough, bumpy skin, which just seemed more like a surface layer, and seemed to have its own organs inside it.
I showed the photos to friends, and they were mystified. One friend sent it to her brother-in-law, who used to work for Fish and Wildlife. No idea.
Luckily, Seattle Aquarium has a Beach Naturalist page, where you can submit photos and questions. I soon got a reply back: it was a twin-sailed salp! A thing I'd never heard of, much less ever seen.
The naturalist kindly sent me a link to the Beach Detective's post about this animal. Take a look - in life, they are so beautiful! Really, look at that link! As she explains, at some points in their life cycle salps are linked together in free-floating colonies. They are free-floating tunicates, and are in the phylum Chordata. That means they are pretty closely related to vertebrates, even though they look like jellyfish! Their scientific name, Thetis vagina, refers to a Greek sea goddess (Thetis) and apparently to their sheath-like shape (not a reference to female anatomy).
Here's a picture of an alive one from the California Academy of Sciences:
I still have so many questions. What are the two appendages for? In the top photo, you can see the remaining appendage on the salp I found (top right side); the other one is gone. Are they the twin-sails of the name? Can salps actively swim, or just float? I'm not even sure which side is the top and which end is the mouth!
Here's another great video from Matt Gieselman. This video makes it look like the appendages are at the tail end - the opposite end from them appears to be a gulping mouth.
I don't mind still having questions - I'm just very happy to have found something new and so very weird on the beach!
I've been reading Pacific Coast Pelagic Invertebrates by David Wrobel and Claudia Mills (lovely book!), and have learned that the dark appendages are definitely at the posterior end (still don't know their function). I also learned that salps have bands of muscle, and can swim by propelling water out either their front or back opening - so they can swim actively!
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